Retro68/gcc/libgo/go/math/log10.go
2017-04-10 13:32:00 +02:00

37 lines
837 B
Go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package math
// Log10 returns the decimal logarithm of x.
// The special cases are the same as for Log.
//extern log10
func libc_log10(float64) float64
func Log10(x float64) float64 {
return libc_log10(x)
}
func log10(x float64) float64 {
return Log(x) * (1 / Ln10)
}
// Log2 returns the binary logarithm of x.
// The special cases are the same as for Log.
func Log2(x float64) float64 {
return log2(x)
}
func log2(x float64) float64 {
frac, exp := Frexp(x)
// Make sure exact powers of two give an exact answer.
// Don't depend on Log(0.5)*(1/Ln2)+exp being exactly exp-1.
if frac == 0.5 {
return float64(exp - 1)
}
return Log(frac)*(1/Ln2) + float64(exp)
}